| With the development of the automobile, motorcycle, electric power, communications and other industries, the demand for lead-acid battery and production increased dramatically, thus driving the vigorous development of Secondary Lead industry. In this paper, with regard to the problems existed in the production process of a lead-acid battery recycling companies, the ion exchange resin was used to eliminated the probably secondary pollution led by a wastewater containing lead yielded in the course of mechanical crushing and hydraulic sorting when its being used as recycling water; in view that a by-product sodium sulfate cannot be used as the chemical raw materials directly because of its lead containing, the chemical precipitation was adopted for the removal of lead.The adsorption effects of five kinds of resin (732, D072,110, of D113, D401) toward Pb2+were investigated with type of H and Na respectively. The results showed that, the adsorption performance of the weak acid and the chelating resin were greatly influenced by the type of resin (H or Na), and the resin type of Na performed a better adsorption behavior. Considering the adsorption capacity and equilibrium time, the resins of732-H and110-H were selected to make a further study.The batch adsorption experiments showed that the solution pH had a obvious influence on the adsorption effect of the two resins, with the acidity increasing adsorption capacity decreased, and110resin seemed to be more susceptible to the influence of the solution pH. In order to increase the adsorption capacity, the pH should be above3. The adsorption isotherm equilibrium experiments demonstrated that the equilibrium adsorption capacity decreased with the temperature increasing. The adsorption isotherm data could be well fitted with the Langmuir isotherm equation and Freundlich isotherm equation. According to Langmuir isotherm equation, the equilibrium adsorption capacity of732resin was1.96mmol/g (406mg/g),110resin4.78mmol/g (989mg/g). Km calculated from the Freundlich equation decreases with temperature increasing, which indicated that the warming was not conducive to adsorption, and n>1showed a preferential adsorption. The adsorption thermodynamic data indicated that two types of resin adsorption behavior toward Pb2+were spontaneous and exothermic reactions along with a increase of the system entropy. The adsorption behavior was in line with the pseudo-first order kinetic model (the adsorption initial phase) and pseudo-second order kinetic model. Weber-Morris model showed that both the particle diffusion and liquid film diffusion were the rate-controlling step of adsorption. The presence of competing ions would reduce the equilibrium adsorption capacity, the greater the concentration of competing ion, the smaller the adsorption capacity. The adverse effects of Ca+were more pronounced than Na+, and110resin had a better selectivity toward Pb2+The column experiments showed that the110resin had a better adsorption effect than732resin, so finally110resin was selected. The optimum conditions for column adsorption were flow rate20BV/h, temperature30℃, the resin type Na; column desorption conditions: desorption agent1.5mol/L HNO3, the flow rate1OBV/h, temperature20℃, the amount5BV.Column adsorption-desorption stability experiments showed that the110resin had a satisfactory stability of adsorption for Pb2+. Under the optimum adsorption-desorption conditions, Pb2+concentration for pre-effluent of2000BV was less than lmg/L.By simulating the mother desulfurization Na2SO4liquor, the solubility of PbSO4in Na2SO4solution was investigated. The results showed that, the solubility of PbSO4increased as the concentration of Na2SO4and temperature increased, this could be due to the combined effect of the salt effect and the common ion effect. Generally, in the pre-desulfurization process, the concentration of Na2CO3was about1mol/L, temperature30-40℃. Under above conditions, the solubility of PbSO4in1mol/L Na2SO4solution was13mg/L (Pb2+). After concentration and crystallization, Na2SO4solid had a lead content of0.0092%, and the content lead presented in the by-product Na2SO4from the plant was0.012%.Compared with the different sediment of lead, Pb(OH)2(PbCO3)2were considered to be the ideal form of precipitation. In view of removal rate and the amount of alkali, Precipitation steps were as follows. The solution of NaOH was used to adjust the pH to10, followed by a further pH adjustment to10.5using Na2CO3solution. The influence of reaction temperature and aging time on the removal rate were investigated, and the best precipitation conditions were reaction temperature20-30℃, aging time30min. The XRD pattern of precipitation was consistent with the Pb3(CO3)2(OH)2XRD pattern (PDF card number:13-0131), which indicated that the structure and composition of this lead-containing precipitate were similar to those of Pb3(CO3)2(OH)2. The solubility of the precipitation in the water and Na2SO4solution had a positive correlation to temperature. The solubility experiment of the precipitation showed that the sediment had a bigger solubility in water than that of in lmol/L Na2SO4solution when temperature was below50℃, and the contrary was observed when temperature was higher than50℃.Under the optimum conditions, the lead removal rate of the actual desulfurization mother liquor was93.8%and the content of lead in the Na2SO4solid obtained after concentration and crystallization was0.00074%which could reach the anhydrous sodium sulfate of analytical grade quality standards (GB/T9853-2008) toward lead control requirement.In summary, the lead removal for the circulating turbid water through ion exchange resin could reduce the possibility of secondary pollution caused by the water in the course of reuse, and the lead removal for the by-product sodium sulfate by chemical precipitation would avoid the pollution generated by the hidden spread of lead. Both of two points mentioned before had some practical significance. |
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